@Eva: Visible light has effects separate from vitamin D. Vitamin D is produced by exposure to ultraviolet radiation. Light boxes work by exposing patients to visible light and are designed to minimize UV exposure to prevent adverse side effects ( http://en.wikipedia.org/wiki/Light_therapy ).

The endorphins will make it more likely that you will spend time in the sun. This is an intelligent system. The brain rewards you for doing something that is good for it. I do feel a good feeling when I am in the sun for a few minutes. I thought maybe it was placebo effect or imagination, but it makes sense now that it was endorphins.

There was some mention somewhere I read that the body produces multiple other products from sun exposure other than just D, none of which has been studied. But they are probably produced for a good reason, one would imagine..

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"The sun may be best known for boosting production of vitamin D, but there are many other UVR-mediated effects independent of this pathway."

Direct immune suppression. Exposure to both UVA and UVB radiation can have direct immunosuppressive effects through upregulation of cytokines (TNF-?? and IL-10) and increased activity of T regulatory cells that remove self-reactive T cells. These mechanisms may help prevent autoimmune diseases.

Alpha melanocyte-stimulating hormone (??-MSH). Upon exposure to sunshine, melanocytes and keratinocytes in the skin release ??-MSH, which has been implicated in immunologic tolerance and suppression of contact hypersensitivity. ??-MSH also helps limit oxidative DNA damage resulting from UVR and increases gene repair, thus reducing melanoma risk, as reported 15 May 2005 in Cancer Research.

Calcitonin gene-related peptide (CGRP). Released in response to both UVA and UVB exposure, this potent neuropeptide modulates a number of cytokines and is linked with impaired induction of immunity and the development of immunologic tolerance. According to a report in the September 2007 issue of Photochemistry and Photobiology, mast cells (which mediate hypersensitivity reactions) play a critical role in CGRP-mediated immune suppression. This could help explain sunlight???s efficacy in treating skin disorders such as psoriasis.

Neuropeptide substance P. Along with CGRP, this neuropeptide is released from sensory nerve fibers in the skin following UVR exposure. This results in increased lymphocyte proliferation and chemotaxis (chemically mediated movement) but may also produce local immune suppression.

Endorphins. UVR increases blood levels of natural opiates called endorphins. Melanocytes in human skin express a fully functioning endorphin receptor system, according to the June 2003 Journal of Investigative Dermatology, and a study published 24 November 2005 in Molecular and Cellular Endocrinology suggests that the cutaneous pigmentary system is an important stress-response element of the skin.

The endorphins will make it more likely that you will spend time in the sun. This is an intelligent system. The brain rewards you for doing something that is good for it. I do feel a good feeling when I am in the sun for a few minutes. I thought maybe it was placebo effect or imagination, but it makes sense now that it was endorphins.

Intense light exposure has many beneficial effects in humans in addition to vitamin D production and the immune effects already noted. Light boxes can mimic the effects of visible sunlight indoors. Light therapy has been used to treat:

@Eva: Visible light has effects separate from vitamin D. Vitamin D is produced by exposure to ultraviolet radiation. Light boxes work by exposing patients to visible light and are designed to minimize UV exposure to prevent adverse side effects ( http://en.wikipedia.org/wiki/Light_therapy ).

From 'The Vitamin D Solution': "Vitamin D made in the skin lasts at least twice as long in the blood as vitamin D ingested from the diet. When you are exposed to sunlight, you make not only vitamin D but also at least five and up to ten additional photoproducts that you would never get from dietary sources or from a supplement.

I don't know if the book goes into greater detail -- this is a quote from Dr. Eades' review. But I Trust Holick.